1. Field of the Invention
The present invention relates to a pattern recognition system, and more specifically to a general pattern recognition system capable of extracting features from not only an image input such as characters and graphic patterns but also any event which varies in time or in space.
2. Description of related art
At present, so-called pattern recognition systems are widely used in an industrial field, for example as apparatuses for reading letters, systems for sorting components or parts and systems for inspecting products. A feature of recognition method common to the conventional systems is to firstly extract various characteristics, which are commonly contained in a group of objects to be recognized, from the input pattern data, and then to categorize the input pattern on the basis of the extracted characteristics.
For this purpose, a processing part of most recognition systems comprises a digital processor and a special circuit which quantitatively extracts specific characteristics, such as a high speed Fourier transformation circuit. In addition, a program for the digital processor must be exclusively designed for each object to be recognized. Such specialization of the recognition system both in hardware and in software has been intended to meet a primary industrial demand for a high-speed recognition.
On the other hand, the specialization of the recognition system makes it necessary to design an system and a program for each recognition object category. As a result, the related techniques are more specialized, and design and modification works have become more complicated. Furthermore, the complication of categorizing processing will lower the reliability of recognition, resulting in more difficult quality control of the pattern recognition systems themselves and in increase of manufacturing cost of the pattern recognition systems.
In addition, users cannot avoid the following disadvantages on the technical point and the cost. First, the technical information on objects themselves to be recognized, which should be held only at the user's side, inevitably flows out to makers of the pattern recognition systems. Secondly, the user is ceaselessly forced to replace the system in use with a new model with improved function every time a model changes.
As described above, the pattern recognition system has even encountered with disadvantages of the specialization and complication.
In this situation, efforts have been made and are now made to simulate a pattern recognition method of a living body.
In response to various stimuli from an external environment, a living body interprets them according to the experience by making use of a brain and a nervous plexus. In fact, however, the living body can not only give one interpretation with reference to its experience and memory but also can give a certain interpretation to inexperienced matters.
The structure of the brain and nervous plexus having the above-mentioned capacity is partially specialized for each recognition object. Most part of the structure, however, is some kind of large-scaled nervous system composed of a large number of single-structural neuropils interconnected with each other. According to the cranial nerve physiology, each of nerve cells organizing the neuropil not only receives the electrical stimuli from several thousands to several ten thousands of other nerve cells, but also generates electrical impulses to itself and to a large number of other nerve cells. The generation of the electrical impulses is called "firing".
The condition of such firing of nerve cells depends on the internal condition of the cells themselves and the stimuli inputted. On the other hand, since it is considered that the whole of a brain executes a certain recognition processing, it can be understood that the firing of even a single nerve cell indicates the result of a partial interpretation processing.
As mentioned above, the nerve cells interchange the electrical impulses each other. The method of applying such impulses can be divided into two manners: the first is to restrain or suppress the firing and the second is to facilitate the firing. The brain can, therefore, be regarded as being a "bang-bang control circuit" having positive feedback control circuits and negative feedback control circuits in a mixed manner.
Furthermore, in the case of a human being, the brain is quite complicated, and composed of more than 10.sup.8 of nerve cells. It is known from the anatomical viewpoint that these cells are interconnected each other, not in a random way but in a regular way in which the same connection patterns composed of several tens to several thousands cells are repeated.
The above description shows the characteristics of the hardware of the brain as a pattern recognition system.
The description will be hereinafter devoted to the software aspect of the action of the brain. The change in spatial and time distribution of the firing of the neuropils caused by the stimuli from the inside and outside of a living body, seems to show the progress of the interpretation processing in the brain, that is, the recognition software and the transfer of the information processed therein.
In general, the features of a brain different from a digital processor are that: (1) the program and data are not stored separately, (2) data processing is executed in completely parallel at various local neuropils and the output can be obtained in harmony as a whole.
A detailed description is made hereinafter for the first feature that program and data are not stored separately. In a digital processor, the program and the data should be regarded to be substantially stored separately, because the processor clearly distinguishes between the data and the instruction in the course of execution of processing based on the program and the data although they are stored mixedly in a memory device. On the other hand, a brain is neither a digital processor of such stored program type nor a discrete logical circuit realized in a conception opposite to that of the above programmed digital processor. The neuropils have a special structure so that the progress of data processing may produce the new experience and consequently a new data processing structure.
As regards the second feature that the parallel data processings on neuropils are in harmony as the whole, a total evaluation is given by the following characteristics. Since the respective firing conditions in local groups of nerve cells are in cooperation to produce one overall harmony, each group of local nerve cells has somehow the information concerning the whole condition and the object to be recognized. Each nerve cell group receives the information from other nerve cell groups with a time delay in comparison with the information which the nerve cell group itself receives directly from an external. Such a feature is a kind of pattern recognition in a wide sense including not only visual recognition but also other recognitions such as audio recognition, and moreover, has no substantial disadvantages inherent to the conventional pattern recognition system of the digital processor type.
Namely, since the store of recognition experiences automatically produces an improved recognition software for possible next recognition operation, it is not necessary to externally give a new software for a possible next object. In addition, although the brain or each neuropil is composed of repeated units of the same structure on the viewpoint of hardware, the brain can cope with the change of the recognition function.